Wow, lots of very interesting arguments to both sides of the debate, but no-one appears to have made the point that:

    my( $foo, $bar ) = @_;
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...is not the same as...

    my $foo = shift;
    my $bar = shift;
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The latter approach modifies the parameter list, they are gone. In the former case, they stay around to haunt you, especially if someone else calls a &foo, and what's left of @_ gets passed along. Talk about effects at a distance. One alternative is to never call &foo, but foo() instead. The other alternative is to use the shift approach. (note to self: remember to adopt tye's approach to fetching parameters).

If the routine is small enough I use $_[0] (in which case what $_[0] should contain should be easy to infer from the sub's name). But not everything can be done with $_[0]. If you want to modify it you must fetch the parameter, viz:

sub x {
  $_[0] =~ s/foo/bar/;
  $_[0];
}
print x('food'), "\n"; # does not work
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print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u'